Mechanical load, systemic and local factors, and certain factors associated with periodontal inflammation produce remodeling of the periodontium in vivo, and are capable of stimulating metabolic activity in tissue-cultured fibroblast and osteoblast cells. While little is known regarding the mechanisms that directly link the cellular and tissue responses, evidence now suggests that alterations in transmembrane conductances mediated by membrane-bound ion channels are associated with early metabolic events during cell activation. The long-term goal of this project is to understand how periodontal tissues respond to both physiological and pathophysiological influences. Within the proposed project period, one aspect of this question will be examined, namely the ionic mechanisms underlying the response of tissue-cultured osteoblast and osteotrophic, i.e., periosteal and periodontal ligament (PDL), fibroblast cells to factors linked to metabolic and morphological changes in the periodontium. These studies will apply patch-clamp recording techniques to monitor single-channel currents in the cell-attached and excised-patch configurations in order to identify and characterize distinct classes of ion channels resident in these cells; ensemble channel activity, i.e., population conductances, a measure of the "systems-level" response of the cells, will be examined using the whole-cell configuration. The first aim is to study the single-channel response properties of ion channels that are activated or deactivated by mechanical deformation of the osteoblast and fibroblast membrane. The second aim is to determine whether there are ligand-gated conductances across the membrane of these cells, and whether ligand-gated conductances are modulated by mechanical stimulation. The third aim is to study the whole-cell currents mediated by the activity of both ligand-gated mechanosensitive ion channels in these cells.